1. Field of the Invention
This invention relates to a heat exchanger for lowering the temperature of exhaust gas emitted from an internal combustion engine, and more particularly to a heat exchanger for lowering the temperature of exhaust gas emitted from a diesel engine operated at work sites in which pulverized coal or mine dust exists.
2. Description of the Prior Art
Vehicles operated at work sites in which pulverized coal or mine dust exists are required to be designed so as not to form ignition energy sources for mine dust floating in the air. At such work sites, exhaust systems of internal combustion engines, in particular diesel engines tends to form ignition energy sources.
The ignition temperature of pulverized coal is about 190.degree. C. If the pulverized coal is exposed to temperatures more than 190.degree. C., there is a risk that it is ignited to cause explosion of mine dust floating in the surrounding air thus not only injuring or killing workers at the site, but also damaging nearby buildings and facilities etc.
The temperature of exhaust gas discharged from exhaust gas systems of internal combustion engines is normally in the range of 500.degree. to 600.degree. C., and particularly in case of turbocharged engines, the surface temperature of an exhaust manifold at the inlet of the turbocharger reaches to 600.degree. to 700.degree. C. in some cases.
As a method of lowering the surface temperature of exhaust pipes and turbochargers, it has commonly been carried out to use a heat insulating material or to thermally insulate by using water cooled pipings. Whilst, no measure has so far been taken to lower the temperature of exhaust gas because there was no strong requirements for it in the past. However, in order to operate vehicles with diesel engine at work sites in which pulverized coal or mine dust exists without causing any hazard, it is essential to lower the temperature of exhaust gas below 190.degree. C.